1. Technical Field of the Invention
The present invention relates generally to electroactive devices. Specifically the present invention relates to the use of electroactive actuators as the driving component of a bending type mechanical actuator capable of producing or experiencing large displacements.
2. Discussion of the Related Art
The related art includes `Rainbow` ferroelectric actuators and sensors, more conventional ferroelectric actuators and sensors, and electromagnetic actuators.
Conventional piezoelectric actuators exhibit limited mechanical displacements. The output of conventional piezoelectric devices is limited by the piezoelectric material's relatively low piezoelectric displacement constant. Thus, conventional devices of reasonable thickness (i.e., on the order of a few millimeters) offer mechanical output motion only in the micrometer range. `Rainbow` actuators, `Moonies`, unimorphic, and bimorphic piezoelectric actuators exhibit greater mechanical output motion. However, even thin ceramic wafers, those on the order of 0.25 mm, which exhibit the maximum observed output motion, provide a displacement limited to approximately 1 mm of motion in the z-direction for a device 3 to 4 centimeters in length.
The related art includes the designs disclosed in U.S. Pat. No. 5,471,721 by Haertling ('721). The first design utilizes a clamshell structure in which two arc shaped actuators are stacked such that their concave surfaces are oriented to face one another. A conductive sheet is located between the actuators. The actuators make contact with the conductive sheet only at the end points of their respective concave faces. The `Rainbow` actuators are not attached to the conductive sheet. The complete assembly functions by allowing the end points of the actuators to slide on the rigid plate. The desired direction of force or deflection for the actuator assembly is perpendicular to the rigid plate. This sliding action results in frictional forces and abrasion of the actuators. The frictional forces created are not uniform over the entire range of motion of the actuators. This nonuniformity displays itself in the way of stiction, the noncontinuous motion of the actuator due to the build up of friction. Multiple clamshell units, separated by rigid plates, may be stacked to provide greater displacement potential.
A second design disclosed by the '721 patent is a stacking of multiple `Rainbow` actuators. The individual actuators are separated by rigid conductive sheets and are oriented such that the convex surface of any `Rainbow` is oriented to face the concave surface of any other `Rainbow` in the stack. As in the previous design the complete assembly functions by the sliding of the actuators on the rigid plate. The desired direction of force or deflection for the actuator assembly is perpendicular to the rigid plate. As with the previously discussed '721 design, this sliding action results in stiction and abrasion of the actuators.
Additionally, these thin ceramic devices require special handling as they are extremely brittle, fragile, and prone to breakage. The delicate nature of these ceramic devices, combined with the limited means of fastening the individual devices in place, severely restricts the range of applications for which the devices are suitable, thus impairing their utility.
Another related art design is the "buzzer" used in audio speakers. The "buzzer" consists of a circular unimorph wafer mounted on a circular diaphragm. The diaphragm is secured along its edge. Electric stimulation of the unimorph causes the diaphragm to displace perpendicular to the plane of the diaphragm. The "buzzer" design does not use pre-stressed unimorphs.
It is accordingly an object of the present invention to provide an electroactive actuator with improved mechanical displacement.
It is another object of the present invention to provide a compliant mounting system for electroactive actuators and sensors.
It is another object of the present invention to improve the efficiency of the actuator.
It is another object of the present invention to remove noise from the output signal of the present invention when it is used as a sensor.
It is another object of the present invention to provide an electroactive actuator with improved durability.
It is another object of the present invention to provide an electroactive actuator with a non-electroactive mounting surface and support layer.
It is another object of the present invention to provide a means of mounting an electroactive device to another electroactive device.
It is another object of the present invention to provide a means of indirectly loading the electroactive element.
It is another object of the present invention to provide a means of changing or modifying the dynamic resonance of the electroactive devices.
It is another object of the present invention to provide a better transfer of mechanical and acoustical energy.
It is another object of the present invention to take advantage of the material characteristics of the support layer and the mass and extension of the support layer and mounting surface.
It is yet another object of the present invention to accomplish the foregoing objects in a simple manner.
Additional objects and advantages of the present invention are apparent from the drawings and specification which follow.